The terms "iniquity", "transgression", and "sin" are a part of a process.
Each of us are on a moving timeline. We are all getting older or aging. It is like we are on a conveyor belt being moved against our wills toward destiny. Each of us can move left or right or stay straight.
It is a bit more dimensional than just a flat surface as, it seems, each of us is also on a terrain where the center is the highest ground and all else is on a sliding scale that degrades the farther we get from center.
In that effort, whatever movement we make, we are either going straight to God or bending away from God, which is either "right" (straight) or "wrong" (bent). If we choose to stay straight, then we have the best vantage point, but the line of balance is thin.
It is not like walking with each foot next to each other. No. It is more like walking each foot in front of the other on a line.
Upon that illustration is my view of right and wrong, iniquity, transgression, and sin painted.
God has his will in each of our lives. We are either lining up with his will or we are not. If we are lining up with his will, then that is being equal with him, in that, we are aligning or paralleling our will with his.
When we are deciding to either go straight or to bend away that is where the process towards sin occurs.
When a person asks, "What is sin?", my questions are something like, "What is God's will for you in your life? Do you know? Have you asked him?"
"Iniquity" means "inequality".
"Transgression" means "to step across".
"Sin" is rather interesting as to what it is. From my research, it is the act of ultimately doing something other than God said to do.
In order to get to sin, there must be the knowledge of iniquity, and the willingness to step away (transgress) from where God wants one to be. Sin results when a person follows through with iniquity and transgression and then commits the actual wrong-doing.
Righteous is being in agreement with God. Iniquity deciding to go to something not in agreement with God, else, unequal to his will. Transgress is deciding to go to the unequality, away from God's will. Sin is being in the unequality ... existing apart from God's will.
Now, it's not like iniquity and transgression are lesser degrees of sin. Without iniquity and transgression there is can not be the result of sin.
Paul stated that law came because of transgressions. Jesus stated "get away from me you workers of iniquity".
It's all bad. None of it is good.